Ống dẫn gió MK4 cải tiến vượt trội

@JuanPuchol_41170's duct is a great upgrade to the Mk4's fan setup; but I was having a hard time printing it without a gap showing up in the one corner (see close up).  So, this is just a mild remix that adds some material in the corner where retraction settings and slicer/printer performance were leaving a gap in the finished part.  Maybe this can be incorporated into the 6.5 or later version of the part.  No other changes to the original model.

Happy Printing!